Ugh, sorry to hear that, Treacle :(
Another one saying don't go crazy on swaddling blankets; save your money for sleeping bags! And seriously, as whatabout said the shops will still be open in September, even 24 hour Tescos; don't feel pressured to buy everything now to 'be prepared'. They really don't need much as newborns.
The only thing I think you ever need more of than you think you will is maternity pads, because take it from me, the lochia even from c-sections is astonishing! You can always take unopened packs back but the NHS will not, contrary to popular belief in some circles, provide pads for you unless it's a dire emergency.
That said, can anyone recommend washable breast pads? I tried some last time and they were absolutely friffing useless and all the milk just ran straight down them. I got on best with the Mothercare comfort fit extra absorbent as they fold them into a semicircle and seal them partway round, so when you open them up they're more cup shaped - if I could find something like that that'd be rad.